Method of preparation of solid



Patented 20, 1949 METHOD OF PREPARATION OF. SOLID ELASTIC METHYLPOLYSILOXANES Murray M. Sprung, Scotla, N. Y., assilmor to General Electric Company, a corporation of N w York No Drawing. Original application June 11, 1946,

Serial No. 676,091. Divided and this application September 17, 1948, Serial No. 49,865

11 Claims. (Cl. 260-465) This application is a division of my copending application Serial No. 676,091, flied June 11, 1946, now U. S. Patent 2,472,629 issued June 7, 1M9, and assigned to the same assignee as'the present invention. This invention is concerned with the preparation of synthetic elastic compositionscomprising dimethyl silicone gums. More' particularly, the invention is concerned with a method of making an elastic gum which comprises contacting a dimethyl silicone (dimethyl polysiloxane), preferably a liquid dimethyl silicone, with a compound selected from the class of compounds represented by the general formulas: i

where R is a hydrocarbon radical selected irom the class consisting of alkyl, aryl. 'aralkyl:.and alkaryl radicals, and X is a halogen, e. g., chicrine,,bromine, fluorine, etc. For brevity, compounds embraced by the above formulas" will hereinafterbe designated generically as "organephosphorushalides. I Two of the more specific embodiments of invention comprise treating a dimethyl silicone with phenoxy phosphoryl dichloride (phenoxy phosphorus oxydichlo'ride) having the iormula or with phenyl phosphonyl dichloride (plieml phosphorus oxydichloride) having the ionnula- O Carl -Cl for a length of time and at a temperature sumcient to convert the said dimethyl silicone to a product having elastic properties, compounding the said product with a filler and a curingor'vulcanizing agent, and thereafter advancing the cure of the filled material under the influence of heat.

Since the organophosphorus halide compounds used in practicing my invention are soluble in the dimethyl silicone, effective concentrations are more easily controlled, and more reproducible results are obtained. Furthermore, these compounds cause the desired elastic gums to form at or near room temperatures, and result in more soluble "(a a. in toluene) products than are ob- 2 tained with catalysts which must be used at elevated temperatures.

The invention is based on my discovery that elastic gums may be prepared by suitable treat ment or dimethyl sillcones; also, that such elastic gums may be compounded with fillers, cure accelerators, 600., and molded or extruded to turn; products exhibiting many of the physical characteristics, such as elasticity, compressibility, etc., of known natural rubber and other synthetic elastomers. 'lne products are characterized by their nexiblllty at low temperatures and particu larly by their heat resistance. The synthetic dimethyl silicone elastomers made from these elastic gums retain their tensile strengths, elongatlon or stretch, flexibility, etc., even when heated for long periods of time at elevated temperatures of, e. g., from to 200 0., without deterioration.

The dimethyl silicones found suitable for the preparation of the elastic gums as well as the synthetic elastomers possessing the above-mentioned properties are those obtained, e. g., by the hydrolysis of a. pure or substantially pure dimethyl dihalogenosilane, e. g., dimethyl-dichlorosilane, or a dimethyl-substituted silane (the methyl groups being joined to the silicon atoms through carbon atoms), whose other two valences are satisfied by radicals which themselves are readily hydrolyzable, for instance hydrogen, amino, alkoxy, aroxy, acyloxy, etc., radicals. While the term dimethyl silicone has been broadly used to designate complex condensation products containing an average of two methyl groups. per silicon atom, it is used herein and in the appended claims to mean a silicone (polysiloxane) in which all or substantially all of the silicon atoms are each connected to two methyl groups.

Various methods may be employed to prepare the dimethyl silicones used in the practice of this invention. For example, substantially pure dimethyl dichlorosilane or dimethyl dichlorosilane containing up to about 2 mol per cent methyl trihalogenosilane, more specifically methyl trichlorosilane, is hydrolyzed in manners now well known in the art. The oily hydrolysis product may then be fractionally distilled to remove the low-boiling materials (trimers, tetramers, etc.) thereby obtaining the higher molecular weight liquid dimethyl silicones, which may then be con tacted with the desired organophosphorus halide to convert it to a dimethyl silicone gum. Optimum properties of the dimethyl silicone gum, as well as of the dimethyl silicone elastomer, are

obtained from hydrolysis products of a mixture comprising substantially dimethyl dichlorosilane and not more than 0.5 mol per cent methyl trlchlorosilane. Stated alternatively, hydrolysis products found useful in the practice of my invention, which hydrolysis products hereinafter are generically referred to as- "dimethyl silicones, are those having a methyl-to-silicon ratio of from 1.98, preferably 1.995, to 2 methyl groups per silicon atom.

More specific directions for the preparation of the dimethyl silicones may be found, e. g., in the copending Patnode applications Serial Nos. 463,813 and 463,815, filed October 29, 1942, each now abandoned; and inAgens application Serial No. 526,473, filed March 14, 1944, now U. S. Patent 2,448,756 issued September 7, 1948. All the foregoing applications have been assigned to the same assignee as the present invention.

The transformation of the liquid, oily'or crystalline dimethyl silicones to the elastic gum stage in accordance with my invention is not exactly understood, but it is believed to be due to a rearrangement of the repetitive units ha of the dimethyl silicone into polymers of extremely high molecular weight which may be best described as elastic gums or, more specifically, dimethyl silicone gums. The properties of these gums may be defined as being elastic, that is, compressible but capable of returning substantially to their original shape when the pressure is removed. Therefore, by my description of the elastic gums (including elastoplastic gums). I intend to exclude from the definition of dimethyl silicone euro-s or elastic gums all materials.

which are lxird and brittle as such. However, it will be apparent to those skilled in the art that the formed elastic gums will include lower as well as higher molecular weight polymers which, if separated into their components, might yield materials varying in properties from thick, sticky masses to very firm, slightly compressible, though still elastic, fractions.

The transformation of the dimethyl silicone to an elastic gum may be accomplished in a number of ways. One method comprises dissolving the organophosphorus halide in the dimethyl silicone and allowing the mixture to stand with or without agitation at normal temperatures for extended periods of time. To hasten the conversion of the dimethyl silicone, the mixture of the dimethyl silicone and the organophosphorus halide may be heated at elevated temperatures ranging from substantially above room temperature up to about 150 C. The time required to convert the dimethyl silicone to the elastic stage will diifer depending, for example, upon the concentration of the organophosphorus halide, the type of dimethyl silicone employed, the temperature at which the conversion is being effected, etc. For example, at room temperatures, from about 2 to 10 or 20 days may be required to convert the dimethyl silicone to an elastic gum having suitable properties. At temperatures of the order of from about to 150 6., the conversion may be effected in from about 5 to 24 hours.

The amount of the organophosphorus halide employed may also be varied over wide limits depending, for instance, upon the reaction conditions and the type of dimethyl silicone employed. Thus, by weight, I may use from 0.1 to as high as ,4 5 or 10 per cent of the organophosphorus halide based on the weight of the dimethyl silicone. Preferably, the amount of the organophosphorus halide is from about 0.5 to 3 per cent of the weight of the dimethyl silicone.

To prepare the synthetic elastomers (synthetic dimethyl silicone elastomers or silicone rubbers), the elastic gum is worked on ordinary mixing (diiferential) rolls used in milling rubber until it attains the desired consistency for molding or extruding. Various fillers, for example, titanium dioxide, and cure accelerators, for example, benzoyl peroxide, in an amount equal to from about 0.5 to 5 or 6 per cent by weight of the dimethyl silicone gum, may be incorporated during this operation. After being formed into the desired shape, for example, under heat and pressure, the cured synthetic dimethyl silicone elastomers may be further cured or vulcanized by heating in an oven until the desired degree of cure is obtained. The latter heat treatment in many cases increases the strength properties of the synthetic elastomer.

The liquid dimethyl silicone which I may use as a starting material may be obtained by several methods. For example, pure or substantially pure dimethyl dichlorosilane may be hydrolysed in water, aqueous hydrochloric acid or in an aqueous solution of sodium hydroxide, etc. Although the method of hydrolysis is not critical, I prefer to use a procedure which yields a liquid product containing a minimum of low-boiling polymers.

Such products are obtained, for example, when the hydrolysis is carried out in, for instance, an aqueous solution of certain metal halides, e. 3., ferric chloride or alkali-metal hydroxides, e. g., sodium hydroxide.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples thereof are given by way of illustration and not by way of limitation. All parts are by weight.

EXAMPLE 1 A dimethyl silicone oil was prepared by slowly adding about 258 parts of a methylchlorosilane comprising substantially pure dimethyldichlorosilane to an amount of water (about 950 parts) sufficient to more than hydrolyze the aforementioned methylchlorosilane. The oily layer which formed was separated, washed with water and sodium carbonate solution, and centrifuged to remove small amounts of solid material and traces of suspended water. Phenoxy phosphoryl dichloride was added in varying amounts to about parts of this dimethyl silicone, and the mixtures were allowed to stand at temperatures ranging from normal to about 100 C. for varying lengths of time. The following table shows the results obtained by contacting the dimethyl sillcone with phenoxy phosphoryl dichloride.

Table I Bank Parts Phe- 1 p19 noxly; Ph{)s- Le i igth of Teltllperii- Character of p ory ime ure P dichloride ducts C. A 0.5 13 days 25 Soft rub B l.0 7days- 25 be. sand 0 1.5 7days 25 Do.

1.0 10 hours.-- 100 Soft, elastic gum. 1.0 14 days 25 Soft, stretchy gum. 1.0 5 days. 25 Soft, elastic gum.

EXAMPLE 2 The elastic products obtained in sample Nos. B,

D, E and F (see Example 1) were milled on differentiai rubber rolls for about 15 minutes with titanium dioxide, lead oxide (to neutralize residual acidity) and benzoyl peroxide dissolved in a small amount of toluene to yield a smooth, homogeneone sheet. The formulation in each case was as After the milling operation, the mass, in each case, was removed from the rolls and pressed into the form or a sheet at about 150 C. for minutes under a pressure of approximately 500 lbs. per e in. The iormed sheets were then cured further by heating them at 150 C. for about 10 hours. The table below shows the tensile strength and elongation at break of these various samples.

Table II Tensileh Flier Cent I No Strengt onga i011 samp e Lbs/sq. in. at Break 100 parts of a liquid dimethyl silicone similar to that used in Example 1 was thoroughly mixed with one part phenyl phosphonyl dichloride, and the mixture was allowed to stand for 49 days at room temperature. At the end of this time a soft, elastic, stretchy gum was obtained. To 100 parts of the elastic gum was added 200 parts titanium dioxide, 10 parts lead oxide (PbO) and 2.5 parts benzoyl peroxide. milled for 20 minutes on cold difierential rubber rolls to yield a smooth, homogeneous sheet. The milled compound was removed from the rolls and pressed into the form of a sheet using the same curing cycle as was employed in Example 2.

This mixture was.

Samples of this sheet were heated for varying lengths of time at different temperatures to determine the efiect of the after-bake on the properties of the material. Table III shows the results of these treatments.

Table III Tensile Per Cent Tem Strength, Elongation Show Hours LbsJsq. in. at Break Hardness No cure- 165 375 24 2 150 450 200 6 150 505 200 18 150 475 150 57 6 200 380 150 54 12 200 430 200 53 18 200 495 175 58 phosphoryl dihalides, e. g., tolyloxy phosphoryl dichloride, ethylphenoxy phosphoryl Idlbromide, etc.; aralkoxy phosphoryl dihalides, e. g. benzyioxy phosphoryl dichloride, phenyleth-oxy phosphoryl dibromide, etc.; alkyl phosp honyl dihalides, e. g., methyl phosphonyl dichloride, propyl phosphonyl dichloride, ethyl phosphonyl dibromide, amyl phosphonyl dichloride, etc. other aryl phosphonyl dihalides, e. g., phenyl phosphonyl dibromide, phenyl phosphonyl difluoride, naphthyl phosphonyl dichloride, etc.; allzaryl phosphonyl dihalides, e. g., tolyl phosphonyl dichloride, ethylphenyl phosphonyl dibromide, etc.; aralkyl phosphonyl dihalides, e. g., benzyl phosphonyl dichloride, phenylethyl phosphonyl dibromide, etc. Methods for preparing the compounds employed in the practice oi this invention may be found in the various literature references available to those skilled in the chemical art, e. g., Beilsteins Handbuch der Organische Chemie (fourth edition).

It will be understood, of course, by those skilled in the art that fillers other than the titanium dioxide disclosed in the foregoing examples may also be used. These include lithopone, zinc oxide, talc, ferric oxide and other finely divided solid materials often employed as fillers for lrnown natural and synthetic rubbers.

The dimethyl silicone gums and the: synthetic dimethyl silicone elastomers prepared therefrom are useful in applications where materials having elastic-like (rubber-like) properties are required, for instance, for gaskets, electrical conductor insulation, shock absorbers, etc. Owing to their extraordinary resistance to deterioration at elevated temperatures, they are particularly useful in applications where natural'rubber or other synthetic elastomers (rubbers) fail due to the deleterious efiect of heat. The synthetic dimethyl silicone elastomers prepared from the dimethyl silicone gums made according to my invention are further endowed with the property of retaining their flexibility at low temperatures.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The method of preparing a solid, elastic, durable methyl-substituted polysiloxane which comprises contacting a. liquid polymeric dimethylsiloxane containing an average from L98 to 2.0 methyl groups per silicon atom and containing up to 2 mol per cent copolymerized monomethylsiloxane with from 1 to 10 per cent, by weight, of an organophosphorus compound corresponding to the general formula where R is a hydrocarbon radical selected from the class consisting of alkyl, aryl, alkaryl and aralkyl radicals, and X is a halogen.

2. The method of preparing a solid, elastic, curable methyl-substituted polysiloxane which comprises contacting a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing up to 2 mol per cent copo lymerized monomethylsiloxane with from 1 to 10 per cent, by weight, of an alkyl phosphonyl dihalide.

3. The method of preparing a solid, elastic, curable methyl-substituted polysiloxane which comprises contacting a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing account up to 2 mol per cent copolymerized monomethylsiloxane with from 1 to 10 per cent, by weight, oi an aryl phosphonyl dihalide.

4. The method of producing a solid, elastic methyl-substituted polysiloxane which comprises reacting 1) a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing up to 2 mol per cent copolymerized monomethylsiloxane with (2) from 0.5 to 3 per cent, by weight, of a phenyl phosphonyl dihalide, the aforesaid reaction between the ingredients (1) and (2) being continued until a solid, elastic product is obtained.

5. The process of producing a solid, elastic methyl-substituted polysiloxane which comprises contacting a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing up to 2 mol per cent copolymerized monomethylsiloxane with from 0.5 to 3 per cent, by weight, phenyl phosphonyl dichloride at a temperature of from 25 to 150 C. until a solid, elastic product is obtained.

6. The process of making a solid, elastic methyl-substituted polysiloxane which comprises (1) treating a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing up to 2 mol per cent copolymerized monomethylsiloxane with from 1 to 10 per cent, by weight, of an organ'ophosphorus compound corresponding to the general formula where R is a hydrocarbon radical selected from the class consisting of allryl, aryl, alkaryl, and aralkyl radicals, and X is a halogen, said treatment being conducted until a solid, elastic product is obtained, (2) compounding the aforementioned elastic product with a filler and benzoyl peroxide, and (3) advancing the cure of the filled material by theapplication of heat.

7. The process of making a solid, elastic methyl-substituted polysiloxane which comprises 1) treating a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing up to 0.5 mol per cent copolymerized monomethylsiloxane with from 0.5 to 3 per cent, by weight, of phenyl phosphonyl dichloride, said treatment being conducted at a temperature of from 25 to 150 C. until a solid, elastic product is obtained, (2) compounding the said elastic product with 8 a filler and benzoyl peroxide, and (3) advancing the cure of the filled material by the application of heat. a

8. A composition or matter adapted for conversion to a solid, elastic curable material, said composition comprising (1) a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing up to 2 mol per cent copolymerized monomethylsiloxane and (2) from 0.1 to 10 per cent, by weight, based on the weight of (1) of an organophosphorus compound corresponding to the general formula where R is a hydrocarbon racidal selected from the class consisting of allcvl, aryl, alkaryl and aralkyl radicals, and- X is a halogen.

9. A composition of matter adapted for conversion to a solid, elastic, curable material, said composition comprising (1) a liquid polymeric dimethylsiloxane containing an average of 1mm 1.98 to 2.0 methyl groups per silicon atom and containing up to 2 mol per cent copolymeriaed monomethylsiloxane and (2) from 0.1 to 10 per cent, by weight, based on the weight or (1), or an alkyl phosphonyl dihalide.

10. A composition of matter adapted for conversion to a solid, elastic, curable material, said composition comprising (1) a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing upto 2 mol per cent copolymerized monomethylsiloxane and (2) from 0.1 to 10 per cent, by weight, based on the weight of (1), of a phenyl phosphonyl dihalide.

11. A composition of matter adapted for conversion to a solid, elastic, curable material, Said composition comprising (1) a liquid polymeric dimethylsiloxane containing an average of from 1.98 to 2.0 methyl groups per silicon atom and containing up to 2 mol per cent copolymerized monomethylsiloxane and (2) from 0.1 to 10 per and Theoretical Chemistry,

cent, based on the weight of (1), of phenyl phosphonyl dichloride.

MURRAY M. BPRUNG.

REFERENCES CITED The following references are oi record in the file of this patent:

Melior: A Comprehensive Treatise on Inorganic vol. VIII, 1928, p. 1046. 

